Test: Clay Material & Soil Structure- 1

Silica tetrahedral unit and octahedral unit are the 2 building blocks of clay mineral.

In silica tetrahedral unit, four oxygen or hydroxyls have the configuration of tetra hadron.

In octahedral unit, aluminum, iron or magnesium atom are enclosed in six hydroxyls having the configuration of an octahedron.

The silicon sheet is represented by trapezoidal symbol, representing the oxygen basal layer and hydroxyl apex layer.

Clay minerals are classified into 3 groups of kaolin, montmorillonite, illite and palygorskite.

The kaolinite structural unit is made up of gibbsite sheet with aluminum atoms at their centers.

Since kaolinite is stable and water is unable to penetrate between the layers, they are held by a fairly strong bond of hydrogen.

The platelets in kaolinite carry negative charges which attract thick layers of adsorbed water thereby producing plasticity.

China clay show the property of plasticity, when mixed with water therefore it can be taken as an example for kaolinite crystal.

The cationic bond of illite is weaker than the hydrogen bond of kaolinite, but is stronger in water bond. Due to this, illite crystal has a great tendency to split in to ultimate platelets.